The present invention relates to rectifier circuits, and is particularly directed to a full wave rectifier or absolute value circuit that provides a comparatively broadband output current that is proportional to the absolute value of input current.
It is well known to implement the full wave rectification or absolute value function using a diode bridge. In addition, a number of absolute value circuits employ single and multiple operational amplifier-based architectures. Non-limiting examples of such configurations are found in the U.S. Patents to Ahmed, U.S. Pat. No. 3,989,997 and Jose et al, U.S. Pat. No. 4,523,105. However, neither of these types of circuits provides current-to-current rectification, and they are not necessarily applicable to DC-coupled applications (the Ahmed patent AC-couples the input signal to the rectifier). For many computational circuits, such as true RMS (root mean squared) converters, it is desirable for the absolute value circuit to provide current-to-current rectification.
In accordance with the present invention, this objective is readily attained by intercoupling a single operational amplifier to a pair of complementary polarity transistors that drive current mirror amplifier stages. The current mirror output stages are configured so as to provide like polarity output currents. The outputs of the current mirror amplifiers are combined so as to produce a composite output current that corresponds to a full wave rectification or absolute value of input current coupled to the operational amplifier. By coupling this full wave rectified current to a load resistor the circuit of the invention produces an output voltage that is the absolute value of an input voltage coupled by way of an input resistor to the operational amplifier.